The present invention relates to a spiral for interconnecting ends of endless belt segments.
Segments of an endless belt have ends provided with sets of terminal fabric loops interdigitatable with one another so that the segments can be connected together by insertion of a pintle into the channel formed by the interdigitated sets of loops of two adjacent belt segments. The sets of loops and the pintle are however subjected to high stresses and strains during operation of the endless belt, so their design and strength are of utmost importance as a loose segment or pintle may cause important damages to the machine or serious injuries to a passer-by.
The sets of loops are frequently provided by spirals seamed at the ends of the belt segments. U.S. Pat. No. 5,915,422 (Fagerholm) shows an example of such a spiral attached at the end of a woven (felt) belt. When viewed sideways, the spiral exhibits a series of V-shaped loops spaced from one another by straight sections especially intended to receive flat filament yarns for attachment of the spiral to the end of the belt section. The interdigitation of two such spirals at the ends of adjacent belt sections is however uneven and unsteady due to the mismatching of the loops between the two interdigitated sets and the large spaces left between the loops for the yarns. Furthermore, the interdigitation is frequently incomplete or partial as a result of the non-complementary shapes of the spirals, so the resulting channel has a reduced size compared to the size of the loops and thus only a small size pintle can disadvantageously be used instead of a larger size one. Furthermore, the pintle is prone to jam in or to deviate out of the channel due to its unevenness and irregularity.
U.S. Pat. Nos. 4,539,730 (Romanski), 4,791,708 (Smolens), EP patent applications Nos. 0,275,656 (Gisourne) published on Jul. 27, 1988, 0,674,041 (Lorenz et al.) published on Sep. 27, 1995, and DE patent application No. 2,059,021 (Andrejewski et al.) published on Jun. 8, 1972 provide examples of spirals of the prior art. Each one of these spirals has its particular features for specific purposes, e.g. straight securing portions for improving the seam, interference fit to facilitate the joining of the spirals, etc. Yet, none of them can be made according to a monofilament diameter, a width, a height and especially a pitch, to fully meet the very requirements of the manufacturer""s endless belts for which they are intended. As a result, they must be stretched or contracted during their assembly with the endless belts. Such longitudinal deformation makes the channel uneven and irregular with the aforesaid problems. It also increases the installation time and effort.
Also, spirals having a pitch of about two times the diameter of the monofilament are very difficult to make due to the shifting of the monofilament during the production of the spiral. No such spirals have apparently ever been successfully produced based on the teachings of the above patents. It is also worth mentioning that known manufactured spirals for interconnecting endless belt segments come in asymmetrical pair, i.e. left and right ones which cannot be interchanged and are also a cause of the aforesaid problems. The currently known spiral designs are limited to a few models which in many cases are fairly unfit for the ever changing models of endless belt segments.
An object of the invention is to provide a spiral for interconnecting ends of endless belt segments using a pintle, which better interdigitates with like spirals than the spirals of the prior art and which allows the use of a larger size pintle for interlocking the spirals together.
Another object of the invention is to provide such a spiral having loops that fully insert down to the bottom of a like spiral, and provide a fairly smooth and regular inner channel facilitating the insertion of the pintle.
Another object of the invention is to provide such a spiral which can be easily manufactured in a large range of sizes and models to fit multiple needs and applications.
Another object of the invention is to provide such a spiral which can be made according to a required pitch for easier assembly with the endless belt, with the pitch possibly ranging over twice the diameter of the monofilament used to form the spiral.
According to the present invention, there is provided a spiral for interconnecting ends of endless belt segments with terminal fabric loops using a pintle. The spiral comprises a series of loops having preformed inverted U-shaped loop portions extending in a transverse direction of the spiral. The loop portions have front and rear parallel legs spaced apart from each other for passage of the pintle therebetween, and an uppermost head bending from and extending between the legs. Preformed U-shaped loop linking portions extend diagonally with respect to a longitudinal direction of the spiral, between lower ends of the front legs and lower ends of the rear legs of the next loop portions respectively. The loop portions are parallel with and spaced from one another by a definite pitch distance in the longitudinal direction of the spiral, adapted to match with the fabric loops at the ends of the endless belt segments and to define openings for interdigitation with a like spiral to form a channel for the pintle without longitudinal deformation of the spirals during interdigitation.
Each loop portion may have projections made out of the spiral on opposite sides of the loop portion in the longitudinal direction of the spiral, for interlocking with like projections on the like spiral.
Preferably, the heads and the loop linking portions have substantially straight portions, so that the channel has a cross-section more rectangular than oblong.
The spiral according to the invention almost fully blends with a like spiral, which leaves more inner space for a larger pintle or for receiving a filling material, while facilitating the spiral assembly.
According to the present invention, there is also provided a process for producing the spiral, wherein a monofilament made of a thermoformable material is wound around a rod having a cross-section reflecting a desired inner shape of the spiral. The wound monofilament is press-shaped against the rod so that it forms a series of loops having the aforesaid features. The press-shaped monofilament is subjected to a heating and cooling fixating cycle.